This invention relates to liquid ring vacuum pumps in general and more particularly to a liquid ring vacuum pump with improved operating characteristics.
A liquid ring vacuum pump for gaseous media of the type which has a machine housing which eccentrically surrounds an impeller and has its end faces closed off by end bells which also support the impeller shaft is known. In such pumps, at least one end bell has separate inlets and outlets for the medium. These are in communication with blade chambers of the impeller, which are closed at their circumference by a liquid ring, through suction and pressure slots in a flat control disc disposed between the end bell and the machine housing. A pressurized liquid canal for sealing liquid is formed in the end bell at a location between the inlets and outlets and is connected to a pressurized liquid feed line. The inlet of a pressurized liquid passage is formed in the control disc below the shaft passage therethrough, in the end face of the disc adjacent the impeller hub and is aligned with the pressurized liquid feed line so that pressurized liquid flows off into the liquid ring, sealing the gap. Such a liquid ring vacuum pump is described in "Vacuum Pumps and Compressors Siemens-System ELMO-F" Nr. E 725/1013.101 (May 79).
Under different operating conditions and modes of operation of liquid ring vacuum pumps, a number of disadvantages occur which to date it has not been possible to completely eliminate or mitigate. Thus, in vacuum pumps which operate with their working fluid extending in circular fashion, either separate pressure booster pumps or, instead, scooping tubes which dip into the rotating liquid ring are screwed into the machine housing on the suction side. In the latter case, erosion damage can occur at the machine housing in the vicinity of the scooping tube dipping into the liquid ring, which affects the life and the proper operation of the vacuum pump adversely.
In addition, gap losses occur in all modes of operation up to about 60 mbar suction pressure. This reduces the efficiency of the vacuum pump. The gap losses can be decreased only to a very limited extent by making the axial play of the impeller smaller because excessively small axial play limits the operating safety.
In vacuum pumps with a revolving liquid, which have a passage in the control disc for the suction liquid, i.e., a circulating water bore hole, appreciable erosion and/or cavitation damage occurs in the region of these passages at the control discs and impellers, which can be retarded only by using high quality material, e.g. CrNi steel, for these parts.
In liquid ring vacuum pumps of the type mentioned at the outset which, in the range of higher suction pressures, are to pump, in addition the gaseous medium, optionally also liquids, more power is required if liquids are also to be pumped, and a degradation of the running properties of the impeller occurs which can lead to premature wear of the bearings of the impeller. To reduce the increase in power requirements, and while maintaining the normal running properties, a separate preliminary separator is built into the suction line ahead of the vacuum pump which separates liquid, that may have already been taken along, from the gaseous medium ahead of the vacuum pump. These measures result in reduced efficiency when only gas is pumped.
The object of the present invention is an improvement of the operating properties, eliminating auxiliary devices which may be necessary in special cases but are expensive and trouble prone, as well as the avoidance of erosion damage in circular operation and/or simultaneous pumping of liquid accumulating on the suction side, in a liquid ring vacuum pump of the type described above,